The Hindu     14.07.2016 

‘Concrete drains prevent groundwater recharge’

Drawing flak:The box-type concrete drains being built by the Mangaluru
City Corporation and the National Highways Authority of India would not
allow rainwater to seep into the ground, say experts.— Photo: H.S.
Manjunath

Even as the Mangaluru City Corporation and the National
Highways Authority of India (NHAI) are busy building concrete box-type
drains along major roads in their jurisdiction, civil engineers and
rainwater harvesting exponents have questioned the rationale behind the
move.

At a time where every inch of urban space is
covered with concrete, the rainwater has no space to percolate down to
the soil and groundwater is not being recharged. In Mangaluru city,
almost every major road is being topped with concrete and shoulder
drains are built using concrete-box technology.

Kannada
Sahitya Parishat’s Dakshina Kannada district president Pradeep Kumar
Kalkura, who is an engineer, said that the concrete box-type drainage
was not suitable for areas where water gets percolated down to the
ground immediately. It might be suitable in regions with black soil
where even a small shower results in water stagnation and creation of
water puddles, he said.

Mr. Kalkura told
The Hindu
that the earlier model of placing granite slabs at the drainage base was
most suited for places like Mangaluru. Under that system, the gaps in
between granite slabs would have allowed percolation of water, he said.
It had twin benefits. On the one hand, it would have recharged the
groundwater and on the other, reduced the inflow to storm water drains.
“Because of concrete drains, heavy rain will result in flash floods as
the rainwater flows at once into major drains. It is unfortunate that
the corporation and the NHAI have introduced a system alien to the
region,” Mr. Kalkura said. Another view was expressed by rainwater
harvesting exponent Shree Padre. According to him, even if concrete
drains are built, the authorities should provide soak pits at regular
intervals so that the rainwater gets absorbed by the soil.

Mangaluru
Mayor Harinath, being aware of adverse effects of box-type drainage,
has been insisting that every drain in his ward, Marakada, should have
space for rainwater percolation. Mr. Harinath told
The Hindu
that for every metre of the drain base, he had got installed PVC pipes to facilitate water percolation.

Not
only such a move would help vegetation in the surrounding area, but
also would recharge the groundwater. Otherwise the excess water flows
somewhere, gets stagnated and becomes breeding ground for many diseases,
he said.

He has instructed the engineering department to follow the model across the city, the Mayor said.